Average Headway
Calculate the average headway (time interval between successive vehicles), h = 3600 ÷ q, dividing 3600 seconds by the flow rate q (vehicles/h). The result, in seconds, is the average time between two consecutive vehicles passing a point. Headway is the inverse of flow: the higher the traffic volume, the shorter the intervals. It is a central concept of traffic flow theory, used in signal design, capacity analysis and car-following models. The smallest safe headway defines the maximum capacity of a lane. Enter the flow rate.
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Headway médio (intervalo veicular)
O headway é o intervalo de tempo entre a passagem de dois veículos consecutivos por um mesmo ponto da via — um dos conceitos microscópicos mais importantes da teoria do tráfego. Em média, ele é simplesmente o inverso do fluxo: h = 3600 ÷ q, com 3600 segundos por hora divididos pela taxa de fluxo q (veículos/h). Quanto maior o volume de tráfego, menores os intervalos: uma via com 1200 veíc/h tem headway médio de 3 segundos. O headway é fundamental por vários motivos. Define a capacidade: a vazão máxima de uma faixa é limitada pelo menor headway que os motoristas mantêm com segurança (cerca de 1,5–2 s na saturação, o que dá ~1800–2000 veíc/h por faixa). Governa os modelos de car-following (perseguição veicular) e a lógica dos sistemas de controle de cruzeiro adaptativo. E é a base do projeto de semáforos, onde o headway de descarga da fila durante o verde determina quantos veículos passam por ciclo. Headways muito curtos indicam direção arriscada (pouco tempo de reação); por isso a 'distância de seguimento' segura é frequentemente expressa em segundos de headway. Informe a taxa de fluxo.
Related Tools
Average Vehicle Spacing
Calculate the average vehicle spacing, s = 1000 ÷ k, dividing 1000 metres by the traffic density k (vehicles/km). The result, in metres, is the average distance between the fronts of two consecutive vehicles in a traffic stream. Spacing is the inverse of density: congested roads have high density and small spacing; free-flowing roads have low density and large spacing. It is the spatial analogue of headway (which is temporal) and relates to speed by s = v·h. The smallest spacing, at jam density, equals the vehicle length plus the minimum gap. Enter the traffic density.
Equivalent Flow (PCE)
Calculate the equivalent flow in passenger car equivalents (PCE), q = Q_cars + Q_heavy × E, adding the car flow to the heavy-vehicle flow multiplied by the equivalence factor E (how many passenger cars each truck or bus equals in road occupancy — typically 1.5 to 3.0). The result, in PCE/h, converts a mixed traffic stream into an equivalent homogeneous one, allowing volumes to be compared and the capacity of roads with different traffic compositions to be computed. Heavy vehicles occupy more space and accelerate more slowly, especially on grades. Enter the car flow, the heavy-vehicle flow and the equivalence factor.
Saturation Flow
Calculate the saturation flow of a signalized approach, S = S₀ × N, multiplying the base saturation flow per lane S₀ (vehicles/h per lane, typically ~1800–1900) by the number of lanes N. The result, in vehicles/h, is the maximum rate of vehicles that can cross the stop line if the signal stayed green continuously and a queue existed — the queue discharge rate during green. It is a central parameter in signal design and intersection capacity, adjusted by lane width, grade, turning and parking factors. Enter the base saturation flow per lane and the number of lanes.
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